1. CPSC 457 Operating Systems
Midterm Review: Practical Questions

2. Q1
Describe the steps that occur when a user program to executes a system call (assuming that there is a system library to wrap the call).
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3. Q2
Describe the steps that occur when the operating system performs a context switch between processes.
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4. Q3
Consider the following table of process, all of which are available at the time of scheduling and arrived in the order in which they are numbered , with the given burst times and priorities (lower numbers are higher priority).
Process
Burst Time
Priority P1
8ms 2 P2
4ms 1 P3
10ms P4
2ms P5
CPSC Tyson Kendon 2016

5. Q3
Draw the Gantt chart and calculate the average turnaround time for the following algorithms.
3a) First Come, First Served
3b) Shortest Job First
3c) Priority
3d) Round Robin (with a 5ms time quantum)
CPSC Tyson Kendon 2016

6. Q4
Consider the following table of process, with the given burst and arrival times
Process
Burst Time
Arrival Time P1
8ms
0 ms P2
4ms
4 ms P3
10ms
6 ms P4
2ms
12 ms P5
18 ms
CPSC Tyson Kendon 2016

7. 4a) Shortest Job First (Non-Preemptive)
Draw the Gantt chart and calculate the average turnaround time for the following algorithms.
4a) Shortest Job First (Non-Preemptive)
4b) Shortest Job First (Preemptive)
4c) Round Robin (with a 5ms time quantum)
4d) A Multi-Level Feedback Queue with 3 queues,
a high priority queue served with Round Robin with a a 2 ms quantum,
a medium priority queue served with Round Robin with a a 6 ms quantum,
a low priority queue served First Come First Served. a job is preempted if a higher priority job is available.
A preempted job is put on the HEAD of its queue.
CPSC Tyson Kendon 2016

8. Q5
5) Recall the formula calculating exponential average:
♣️n+1 = ♥️tn + (1 - ♥️) ♣️n
For a process with the following real burst times, an initial estimated burst time of (4 ms) and a memory factor () of .5 calculate estimated burst times for each n. (Round to the nearest integer ms) 1 2 3 4
Estimated Burst
5ms
Real Burst
10ms
2ms
8ms
3ms
12ms
CPSC Tyson Kendon 2016